I have some experience with this.
You're probably okay with a standard dark suit unless that is somehow related to the person's death. Like if you were going dark suit shopping that day, and you picked him up and got into a car crash. Or if it was a child that you were playing hide and seek with and it suffocated under a dark suit.
That's probably enough examples. A kid died in that last one.
Short Answer: What you don't want to wear is a t-shirt that says 'Sorry, my bad.' Or crocs. Never fucking wear crocs.